9. Numeric and Mathematical Modules
***********************************

The modules described in this chapter provide numeric and math-related
functions and data types. The "numbers" module defines an abstract
hierarchy of numeric types. The "math" and "cmath" modules contain
various mathematical functions for floating-point and complex numbers.
The "decimal" module supports exact representations of decimal
numbers, using arbitrary precision arithmetic.

本章记录以下模块：

* 9.1. "numbers" --- Numeric abstract base classes

  * 9.1.1. The numeric tower

  * 9.1.2. Notes for type implementors

    * 9.1.2.1. Adding More Numeric ABCs

    * 9.1.2.2. Implementing the arithmetic operations

* 9.2. "math" --- Mathematical functions

  * 9.2.1. Number-theoretic and representation functions

  * 9.2.2. Power and logarithmic functions

  * 9.2.3. Trigonometric functions

  * 9.2.4. Angular conversion

  * 9.2.5. Hyperbolic functions

  * 9.2.6. Special functions

  * 9.2.7. Constants

* 9.3. "cmath" --- Mathematical functions for complex numbers

  * 9.3.1. Conversions to and from polar coordinates

  * 9.3.2. Power and logarithmic functions

  * 9.3.3. Trigonometric functions

  * 9.3.4. Hyperbolic functions

  * 9.3.5. Classification functions

  * 9.3.6. Constants

* 9.4. "decimal" --- Decimal fixed point and floating point
  arithmetic

  * 9.4.1. Quick-start Tutorial

  * 9.4.2. Decimal objects

    * 9.4.2.1. Logical operands

  * 9.4.3. Context objects

  * 9.4.4. Constants

  * 9.4.5. Rounding modes

  * 9.4.6. Signals

  * 9.4.7. Floating Point Notes

    * 9.4.7.1. Mitigating round-off error with increased precision

    * 9.4.7.2. Special values

  * 9.4.8. Working with threads

  * 9.4.9. Recipes

  * 9.4.10. Decimal FAQ

* 9.5. "fractions" --- Rational numbers

* 9.6. "random" --- Generate pseudo-random numbers

  * 9.6.1. Bookkeeping functions

  * 9.6.2. Functions for integers

  * 9.6.3. Functions for sequences

  * 9.6.4. Real-valued distributions

  * 9.6.5. Alternative Generator

  * 9.6.6. Notes on Reproducibility

  * 9.6.7. Examples and Recipes

* 9.7. "statistics" --- Mathematical statistics functions

  * 9.7.1. Averages and measures of central location

  * 9.7.2. Measures of spread

  * 9.7.3. Function details

  * 9.7.4. 异常
